Gaseous electric discharge device



April 1939- w. ELENBAAS ET AL 2,152,983

GASEOUS ELECTRIC DISCHARGE DEVICE Filed May 17, 1935 94 (SW 9 I.

nCCFuedJ 23W ATTORNEY Patented Apr. 4,1939

GASEOUS ELECTRIC DISCHARGE DEVICE Willem Elenbass, Gottfried BrunoJonas, and Aart van Wyk, Eindhoven, Netherlands, assignors to GeneralElectric Company, a corporation of New York Application. May 17; 1935,Serial No. 22,070

' In Gelgnany May 18, 1934 4 Claims. (Cl. 176-122) in creasingtemperature the absorption band of glass is shifted towards longerwavelengths of the spectre, that is to say the more strongly the closerto shorter wavelengths of the spectre the maximum of the absorption bandislocated at ordinary temperatures (Wien-Harms, Handbuch derExperimental-.physik, 1928, volume 19, page 335). Thus, for example, ithas been i'ound that glasses of'the compositions? 2 10.5% of ZnO, or

(2) 76.6% of SiOz, 15% Of Bros and 8.4% of K20,

which are satisfactorily transparent to ultraviolet light at ordinarytemperatures transmit at high 25 temperatures only few ultraviolet rays.At ordinary temperatures and with a thickness 011 mm. the firstmentioned glass of the composition indicated under (1) transmits thewavelength '0! 2967 A. for 43% and at 600 C. for 12.5%. -With 30 theglass 01 the composition indicated under (2) the transmissibility isunder the same conditions 50% and only 4.5% respectively.

According to the invention, sources of electric light or the abovementioned type are furnished 35 -with bulbs constituted by glassconsisting of 8102,

B20; and A1203, containing substantially no alkalioxide, for exampleless than 1%, and having a softening point of higher than 600 C. Ifdesired. an alkaline earth oxide such as CaO may be added 40 to thesmelt. Use should preferably be made of glasses of this kind which havea content of SiO:

higher than 10%. As glasses suitable for use in the sources of lightaccording to the invention may be mentioned, for example, compositions isuchas (3) 77.2% of $102, 10.7% of A1103, 5.4% or CaO and 7.0% of B20:or

(4) 84.4% of S102, 4.4% '0f A1203, 0.4% of CaO and 10.8% 01320:.

0, 5 Said glasses may contain slight amounts of other substances whichhave an only immaterially injurious eilect on the optical properties andon the softening point.

'55, Glasses of this me have already been described I in themselves, forexample'in connection with the fact that they have a low coefllcient ofexpansion and furthermore on account of their capability of being sealedto quartz, which properties have been utilised withsuch sources ofelectric 5 light to which the invention relates but in which just thatportion of the bulb which allows the light to pass consisted of quartzglass.

However, as mentioned already, the said kinds of glass although having ahigh softening point have not been employed-in these sources of light asthe constituent material for the envelope.

Experiments which led to the present invention have shown that thet'ransmissibility of these kinds of glass in the ultraviolet region ofthe 15.

spectrum is very satisfactory even at a high operating temperature ofthe above-mentioned sources of light, although with these glasses, too,the transmissibility decreases when the temperature 'increases. Thedecrease in 'transmissibility occurring at said high operatingtemperature does however not entail any inconvenience in practice. Thus,it has been found that at 600 C. and with a thickness of 1 mm. theglasses utilised in accordance with the invention transmitthe wavelength of 2967 A. for more than '70%. These kinds of glass may beemployed with particular advantage for so-called high pressure mercuryvapour discharge tubes which may comprise one or more cathodes of goodelectron emitting capacity and in which the discharge takes place inmercury vapour under high pressure. A. discharge in mercury vapour underhigh pressure" has to be understood to mean a discharge in mercuryvapour which has the property of being contracted instead of filling thewhole of the cross-sectional area of the tube. It has been stated thatthe glass utilised in accordance with the invention is satisfactorilyresistant to the influence of the high pressure mercury vapourdischarge.

The invention will be explained more' fully with reference to theaccompanying drawing which diagrammatically represents by way of exampleone mode of realisation.

Figure 1 represents a high pressure mercury vapour discharge tubeconstituted by a glass vessel I consisting of one of the glasses of thecompositions indicated under 3 or I. Said tube contains cathodes 2 orgood electron emitting capacity and has pinches 3 into which currentsupply wires 4 are sealed. The glass vessel I contains a slight amountof mercury.

What we claim is: a 1. A gaseous electric discharge device comprising-acontainer, electrodes sealed therein, a gaseous atmosphere therein, saidcontainer comprising a radiation transmitting glass consisting ofsilica, alumina, alkaline earth oxide and boric oxide, the silicacontent being less than about 85% and morethan 70%, the alumina contentbeing less than 11% and more than 4%, the

alkaline earth oxide content being less than 6% and more than 0.3% andthe boric oxide content being less than 11% and more than 6%.

2. A gaseous electric discharge device comprising a container,electrodes sealed therein, a gaseous atmosphere therein, said containercomprising a radiation transmitting glass containing:-

Percent Silica (SiOa) v 77.2 Alumina (A1203) 10.? Calcium oxide (CaO)5.4 Boric oxide (B203) 7.0

3. A gaseous electric discharge device compris ing a container,electrodes sealed therein, a gaseous atmosphere therein, said containercomprising a radiation transmitting glass containing:-

Percent Silica (310:) 84.4 Alumina (A1209 4.4 Calcium oxide (090) 0.4Boric oxide (B203) 10.8

wILLEM ELENBAAS. oom'nmn ammo JONAS. v AART vm wm

